For starters, you can check what is the cause of resonance, most likely is something you can change, like inlet/outlet velocity. You could consider inlet nozzle inserts / difusers, depending also on the current roVsq. If the bundle is removable, perhaps some additional tube support may be considered. If nothing else helps, scrap the exchanger and start all over again, minus the resonance.
Cheers,
gr2vessels